1. Field of the Invention
The present invention relates to a device for measuring the radiation temperature of a melt in vacuum, which uses a pyrometer.
2. Description of Related Art
In measuring the temperature of molten samples, in particular of metals, in a vacuum, there is a problem that sample material in a vapor state will be deposited on the wall of the vacuum chamber or the window of the pyrometer. In this case, the member, initially permeable to the radiation, will quickly become impermeable to the radiation because of the evaporation, and will be unfit for further pyrometric use.
From Japanese Patent 60-57224 A, in: Patents Abstract of Japan, Vol. 9 (1985), No. 186 (117 P 377), a device for measuring the radiation temperature of a melt in vacuum is known wherein the radiation thermometer is shielded against vaporous matter by a perforated screen with a central passage. The shielding cannot be complete, since the pyrometer is still orientated directly towards the melt and, thus, is still evaporated. Moreover, only a comparatively small amount of the radiation emitted by the melt reaches the pyrometer, due to the shielding, so that the temperature measurement is rather inexact.
It is an object of the invention to provide a device of the type mentioned above, wherein the present pyrometer is reliably protected against an evaporation by the melt material, although a comparatively large amount of the radiation is measured.